704 Binary Search

704 Binary Search

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

class Solution(object):
    def search(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        left = 0
        right = len(nums)-1
        while left <= right :
            # use (right - left)/2 to prevent overflow caused by a large value
            # '//' floor divide, get int value
            middle = left + (right -left) // 2 
            if nums[middle] > target:
                right = middle - 1
            elif nums[middle] < target:
                left = middle + 1
            else:
                return middle
        return -1

Time Complexity: O(logn)

Space Complexity: O(1)